The Research On A Novel Tunable And Highly Stable Mode-locked Laser In Near Infrared Band

The laser is one of the greatest inventions in the twentieth century.Among them,solid laser is widely used,especially in metal processing,medicine,industrial manufacturing and other aspects,such as eye surgery,red,green and blue?RGB?light source laser printer and projector,environmental measurement and so on.In history,the scientists used single crystal or glass is used as a solid state laser gain medium,is the first successful ruby laser designed by Maiman in 1960,and since 1964,when people use the Nd:YAG(Nd:Y₃Al₅O₁₂)single crystal successfully produce continuous-wave laser oscillation at room temperature,the use of single crystal solid laser design has made much progress.The transparent ceramic laser is a promising candidate gain medium because of its advantages over single crystal laser.Firstly,ceramics can be produced in large quantities.Secondly,they can provide a gain medium for high beam quality fiber lasers or can be made into complex composite laser media.In addition,ceramics can be doped with a large number of laser active ions evenly.They can also be used in the manufacture of new laser materials,such as sesquisoxide,which cannot be produced in the traditional melt growth process.This new laser material has the advantages of strong anti-laser damage ability and long life,and has a broad application prospect in the field of high power density laser.So using transparent ceramic material takes place of single crystal material as laser gain medium has become a research hotspot.In this paper,based on the new laser gain solid material,the influence factors of the matrix material on the spectrum,thermophysical property and thermoptric property are analyzed theoretically,and the rate equation description of the energy level system is given theoretically in detail,so as to predict the laser output characteristics.Subsequently,continuous wave ceramic lasers and tunable ceramic lasers were designed and constructed respectively to study the optical and thermal properties of Yb:YAG(Yb:Y₃Al₅O₁₂)and Yb:YSAG(Y₃SC_xAl_5-XO₁₂)ceramics with different thickness of the same substrate.Because of the poor stability of solid-state lasers,it is necessary to develop a highly stable mode-locked laser.Therefore,based on the semiconductor saturable absorption mirror technology,the ultra-short mode-locked pulse output with all-polarization-maintaining fiber structure is realized.The specific research contents of this paper are as follows:1.In terms of Yb³⁺doped laser gain solid material,the main advantages of Yb³⁺as an active ion compared with Nd³⁺are high efficiency,low heat generation and small quantum defects.Then ytterbium was selected as the doped element.By comparison,it was found that the doped semi-oxide in the transparent ceramic matrix material increased the absorption cross section and thermal conductivity coefficient,thus enhancing the ceramic anti-laser damage ability.Then the rate equation description of the energy level system is given theoretically in detail to predict the laser output characteristics.In the end,the composition of the laser and the principle of laser generation are introduced,which provides a theoretical basis for further research on the laser characteristics of ytterbium doped ceramic solid laser.2.In the study of ytterbium doped ceramic continuous-wave laser,continuous wave ceramic laser and tunable ceramic laser were designed and constructed respectively,In the Yb:YSAG ceramic laser,we obtain a continuous-wave laser whose output power was 1.79W,the corresponding slope efficiency was 19.7%,and the tunable spectrum range was over 19nm.3.As the solid state laser has the shortcoming of poor stability,so the research on high stable mode-locked laser is necessary,first of all,by studying the fiber mode-locking laser mechanism,combined with the theoretical analysis and based on semiconductor saturable absorber,we formed all polarization-maintaining erbium-doped fiber mode-locked oscillator,by optimizing the erbium-doped fiber length and matching the positive and negative dispersion optical fiber length,we abtain a femtosecond pulse,whose average power is 119mW,pulse energy is 1.43nJ,and pulse width is 73fs.The integrated design with anti-environment interference ability was further completed,and the precise locking between the oscillator repetition frequency and rubidium atomic clock was realized.The standard deviation of frequency after the repetition frequency stabilized was 160?Hz.4.Finally,two different mode-locked pulses with a spectral overlap repetition,whose frequency difference is 13kHz,were obtained by using SESAM and grating.Two mode-locked pulses with different repetition rates based on the same laser are an alternative to highly coherent dual-comb sources.A single cavity of a double-pulse laser not only reduces the system volume,but also enhances the coherence of the two output mode-locked pulses.